Gyroid Morphologies in Single-Ion Conducting Polymers and the Consequences for Ion Conductivity

The morphology of self-assembled ionic aggregates influences the ion transport in single-ion conducting polymers. Recently, our group reported that polymers with sulfosuccinate units containing sulfonate groups with their counterions (Li⁺, Na⁺, and Cs⁺) and precisely separated by 23 methylene units form ordered ionic aggregate morphologies (layered, gyroid, and hexagonal). In these ionomers, the gyroid morphology exhibits higher ion conductivity than layered and hexagonal ionic aggregates morphologies, demonstrating the importance of bicontinuous ion-containing channels for enhanced ion conductivity. These gyroid morphologies were reported at relatively high temperatures (120°C - 130°C) that are coincident with the melting point of the crystalline polyethylene unit. To produce the gyroid phase in a lower temperature range, polymers with shorter polyethylene units are being explored and results will be discussed using a phase diagram with volume fraction of sulfosuccinate units (f_polar) and temperature, similar to conventional block copolymer phase diagrams. This study endeavors to provide design strategies for single-ion conducting polymers with controlled ionic aggregate morphologies and enhanced ion conducting properties.